230 
MORPHOLOGY 
nosperm groups, but in addition to these gymnospenn tracheids there 
are also true vessels of the angiosperm type. 
Staminate strobili. The stami- 
nate strobili are made up of pairs 
of decussate bracts, which are im- 
bricate in Ephedra (fig. 513) and 
Tumboa (fig. 519), and connate in 
Gnetum (fig. 523). In the axils 
of these bracts are the so-called 
staminate flowers. In Ephedra 
and Gnetum a staminate flower 
FIG. 520. Tumboa: staminate "flower" consists of an axis bearing at its 
(with bracts removed), showing the six tri- tip two or more sporangia (figs, 
sporangiate stamens united below, and the \ j 
sterfleovulewithlongandtwistedmicropylar 513, 524), and invested below by 
tube. Adapted from HOOKER. two or four bracts, which are free 
or coalescent in a tube. In Tumboa 
the structure is very different and quite remarkable. Within the in- 
vesting bracts there is a whorl of six united (monadelpJwus) stamens, 
each of whose free tips bears three sporangia; 
and within the cycle of stamens there is a cen- 
tral (terminal) sterile ovule, whose remarkably 
long micropylar tube is spirally coiled and 
broadly flaring at the tip (fig. 520). This re- 
markable structure indicates that the ancestors 
of Tumboa had flowers that contained function- 
ing stamens and ovules, and that in the case of 
Tumboa staminate and ovulate flowers arose by 
the disappearance of ovules in certain flowers, 
and of stamens in others. No such close 
association of stamens and ovules is known 
among gymnosperms, except in Bennetti tales, 
where they occur in the same strobilus. 
In attempting to interpret the staminate 
strobilus of the Gnetales, it is evident that the ovulate " flower ." showing 
. , the enveloping and winged 
microsporangia are borne upon secondary axes bracts, the two integuments 
(which are the so-called flowers), and therefore (the inner forming the long 
the strobilus is compound. ' In Cordaitales and micr py lar tube), and the 
,,_,...., , nucellus containing the em- 
m certain of the Comferales there are compound bryo sac ._ Ad apted from 
ovulate strobili, but only in Gnetales do com- STRASBURGER. 
FIG. 531. Tumboa: 
